1. Field of the Invention
This invention relates to atherectomy catheters, and more specifically to atherectomy catheters having a composite tissue cutter formed with a cutter and a sensor mount.
2. Previous Art
Atherosclerosis is a condition characterized by the deposit of fatty deposits (atheromas) which adhere to the internal lining of human blood vessels. Atherosclerosis manifests itself in a variety of ways. Angina, hypertension, myocardial infarction, and strokes may result from untreated atherosclerosis.
Regions of a blood vessel blocked by atheroma, plaque, or other material are called stenotic regions. The blocking material is known as stenotic material or plaque. Stenotic material is often relatively soft and tractable. However, stenotic material can also be calcified and hard. Plaque may be harder than ordinary tissue and may firmly adhere to the walls of blood vessels and other biological conduits.
Atherectomy catheters are used to remove stenotic material from the inside of blood vessels. A typical atherectomy catheter has a distal end which inserts into a biological conduit to remove plaque. A housing with a nose cone attaches to the distal end. A cutter is enclosed in the housing. A cutter torque cable extends within the catheter and attaches to the cutter. The cutter cuts stenotic material from the inside of a blood vessel in response to movement of the cutter torque cable when the catheter is appropriately positioned.
During an atherectomy procedure, an atherectomy catheter is inserted into the femoral artery of a patient by a physician. The physician manipulates the catheter and positions the housing of the catheter adjacent a stenotic region having stenotic material within the blood vessel. The cutter is manipulated for the removal of stenotic material. The removed stenotic material is captured by the nosecone of the catheter.
Atherectomy catheters having tissue cutters have enjoyed substantial success and acceptance in the medical community. Atherectomy catheters have been most effective when used for the removal of relatively soft (e.g. non-calcified) stenotic material. The removal of hard material such as calcified plaque, however, has been more problematic. When the cutter of an atherectomy catheter encounters calcified plaque, for example, the cutting edge of the cutter becomes dull. Hardened plaque is difficult to remove with a dull cutter.
Cutters fabricated from harder materials have been developed to minimize dulling. The harder materials enable cutters to cut hardened calcified plaque without dulling or deforming. Examples of such cutters are disclosed in U.S. Pat. No. 5,507,760, Issue Date, Apr. 16, 1996 to Wynne et al., entitled "Cutter Device", the disclosure of which is incorporated herein by reference.
The state of the art has advanced. The use of cutters having ultrasonic imaging sensors is now known. An example of a cutter having an ultrasonic imaging transducer is described in U.S. Pat. No. 5,000,185, issued Mar. 3, 1991 to Yock. Ultrasonic imaging sensors perform various useful functions such as safely guiding an atherectomy device through a vascular system, for example. Ultrasonic imaging sensors inspect the stenotic material to be cut and have proven to be useful when employed with devices such as atherectomy catheters.
Proper attachment of a sensor to the cutter of an atherectomy device should align the sensor with respect to the cutter and protect the sensor from damage. Attachment of the sensor is effectively accomplished by machining a portion of the cutter and attaching the sensor to the machined portion of the cutter. In this way, a firm base for attachment of the sensor is established. Machining is difficult, however, for a variety of reasons. The hardness of the atherectomy cutters in combination with the very small size of atherectomy cutters makes machining of the cutters difficult. Adapting a hard cutter to house a sensor is expensive and impractical when accomplished by common machining methods.
It is desirable to provide a device having a cutter which is capable of cutting calcified deposits without dulling. It is also desirable to provide a device which is adapted to hold a sensor which can guide the device through the vasculature of a patient.